Remove magic numbers and strings from receipt printer implementations

c/src/printer.c

@@ -2,6 +2,24 @@
 #include <string.h>
 #include "printer.h"
 
+// Constants for receipt formatting
+#define QUANTITY_THRESHOLD 1
+#define PRICE_DECIMAL_PLACES 2
+#define WEIGHT_DECIMAL_PLACES 3
+#define INTEGER_DECIMAL_PLACES 0
+
+// Format strings
+#define PRICE_FORMAT "%.2f"
+#define WEIGHT_FORMAT "%.3f"
+#define INTEGER_FORMAT "%.0f"
+
+// Display strings
+#define UNIT_PRICE_INDENT "  "
+#define MULTIPLICATION_SYMBOL "*"
+#define TOTAL_LABEL "Total:"
+#define WHITESPACE_CHAR ' '
+#define NEWLINE "\n"
+
 void printReceiptItem(char *buffer, struct receipt_item_t *item);
 
 void printDiscount(char *buffer, struct discount_t *pDiscount);
@@ -15,46 +33,46 @@ void print_receipt(char* buffer, struct receipt_t* receipt) {
     for (int i = 0; i < receipt->discountCount; ++i) {
         printDiscount(buffer, &receipt->discounts[i]);
     }
-    sprintf(buffer + strlen(buffer), "\n");
+    sprintf(buffer + strlen(buffer), NEWLINE);
 
     print_total(buffer, receipt);
 
 }
 
 void printReceiptItem(char *buffer, struct receipt_item_t *item) {
     char price[MAX_NAME_LENGTH];
-    sprintf(price, "%.2f", (*item).totalPrice);
+    sprintf(price, PRICE_FORMAT, (*item).totalPrice);
     char name[MAX_NAME_LENGTH];
     sprintf(name, "%s", (*item).product->name);
 
     char line[LINE_LENGTH];
     print_line(line, name, price);
     sprintf(buffer + strlen(buffer), "%s", line);
 
-    if (item->quantity != 1) {
+    if (item->quantity != QUANTITY_THRESHOLD) {
         char line2[LINE_LENGTH];
         if (item->product->unit == Each) {
-            sprintf(line2, "  %.2f*%.0f", item->price, item->quantity);
+            sprintf(line2, UNIT_PRICE_INDENT PRICE_FORMAT MULTIPLICATION_SYMBOL INTEGER_FORMAT, item->price, item->quantity);
         } else {
-            sprintf(line2, "  %.2f*%.3f", item->price, item->quantity);
+            sprintf(line2, UNIT_PRICE_INDENT PRICE_FORMAT MULTIPLICATION_SYMBOL WEIGHT_FORMAT, item->price, item->quantity);
         }
-        sprintf(buffer + strlen(buffer), "%s\n", line2);
+        sprintf(buffer + strlen(buffer), "%s" NEWLINE, line2);
     }
 }
 
 void print_total(char *buffer, struct receipt_t *receipt) {
     char total[MAX_NAME_LENGTH];
-    sprintf(total, "%0.2f", total_price(receipt));
+    sprintf(total, PRICE_FORMAT, total_price(receipt));
     char total_line[LINE_LENGTH];
-    print_line(total_line, "Total:", total);
+    print_line(total_line, TOTAL_LABEL, total);
     sprintf(buffer + strlen(buffer), "%s", total_line);
 }
 
 void printDiscount(char *buffer, struct discount_t *discount) {
     char name[LINE_LENGTH];
     sprintf(name, "%s(%s)", discount->description, discount->product->name);
     char price[MAX_NAME_LENGTH];
-    sprintf(price, "%.2f", discount->amount);
+    sprintf(price, PRICE_FORMAT, discount->amount);
 
     char line[LINE_LENGTH];
     print_line(line, name, price);
@@ -67,9 +85,9 @@ print_line(char *buffer, const char *key, const char *value) {
     int whitespace_length = LINE_LENGTH - strlen(key) - strlen(value);
     char whitespace[whitespace_length];
     for (int i = 0; i < whitespace_length -1; ++i) {
-        whitespace[i] = ' ';
+        whitespace[i] = WHITESPACE_CHAR;
     }
     whitespace[whitespace_length-1] = '\0';
 
-    sprintf(buffer, "%s%s%s\n", key, whitespace, value );
+    sprintf(buffer, "%s%s%s" NEWLINE, key, whitespace, value );
 }

c/src/supermarket.c

@@ -3,6 +3,15 @@
 #include <stdio.h>
 #include "supermarket.h"
 
+// Constants for special offers
+#define THREE_FOR_TWO_QUANTITY 3
+#define TWO_FOR_AMOUNT_QUANTITY 2
+#define FIVE_FOR_AMOUNT_QUANTITY 5
+#define TWO_FOR_AMOUNT_MIN_QUANTITY 2
+#define THREE_FOR_TWO_MIN_QUANTITY 2
+#define FIVE_FOR_AMOUNT_MIN_QUANTITY 5
+#define PERCENT_DIVISOR 100.0
+
 struct product_t* product_create(char* name, enum unit unit) {
     struct product_t* product = malloc(sizeof(*product));
     strncpy(product->name, name, sizeof(product->name) - 1);
@@ -76,34 +85,34 @@ void handle_offers(struct cart_t* cart, struct receipt_t* receipt, struct specia
             int x = 1;
 
             if (offer->type == ThreeForTwo) {
-                x = 3;
+                x = THREE_FOR_TWO_QUANTITY;
             } else if (offer->type == TwoForAmount) {
-                x = 2;
-                if (quantityAsInt >= 2) {
-                    double total = offer->argument * (quantityAsInt / x) + quantityAsInt % 2 * unitPrice;
+                x = TWO_FOR_AMOUNT_QUANTITY;
+                if (quantityAsInt >= TWO_FOR_AMOUNT_MIN_QUANTITY) {
+                    double total = offer->argument * (quantityAsInt / x) + quantityAsInt % TWO_FOR_AMOUNT_QUANTITY * unitPrice;
                     double discountN = unitPrice * quantity - total;
                     char description[MAX_NAME_LENGTH];
-                    sprintf(description, "2 for %f", offer->argument);
+                    sprintf(description, "%d for %f", TWO_FOR_AMOUNT_QUANTITY, offer->argument);
                     discount = discount_create(description, -discountN, &product);
                 }
             } if (offer->type == FiveForAmount) {
-                x = 5;
+                x = FIVE_FOR_AMOUNT_QUANTITY;
             }
             int numberOfXs = quantityAsInt / x;
-            if (offer->type == ThreeForTwo && quantityAsInt > 2) {
-                double discountAmount = quantity * unitPrice - ((numberOfXs * 2 * unitPrice) + quantityAsInt % 3 * unitPrice);
+            if (offer->type == ThreeForTwo && quantityAsInt > THREE_FOR_TWO_MIN_QUANTITY) {
+                double discountAmount = quantity * unitPrice - ((numberOfXs * TWO_FOR_AMOUNT_QUANTITY * unitPrice) + quantityAsInt % THREE_FOR_TWO_QUANTITY * unitPrice);
                 char description[MAX_NAME_LENGTH];
-                sprintf(description, "3 for 2");
+                sprintf(description, "%d for %d", THREE_FOR_TWO_QUANTITY, TWO_FOR_AMOUNT_QUANTITY);
                 discount = discount_create(description, -discountAmount, &product);
             }
             if (offer->type == TenPercentDiscount) {
                 char description[MAX_NAME_LENGTH];
                 sprintf(description, "%.0f%% off", offer->argument);
-                discount = discount_create(description, -quantity * unitPrice * offer->argument / 100.0, &product);
+                discount = discount_create(description, -quantity * unitPrice * offer->argument / PERCENT_DIVISOR, &product);
 
             }
-            if (offer->type == FiveForAmount && quantityAsInt >= 5) {
-                double discountTotal = unitPrice * quantity - (offer->argument * numberOfXs + quantityAsInt % 5 * unitPrice);
+            if (offer->type == FiveForAmount && quantityAsInt >= FIVE_FOR_AMOUNT_MIN_QUANTITY) {
+                double discountTotal = unitPrice * quantity - (offer->argument * numberOfXs + quantityAsInt % FIVE_FOR_AMOUNT_QUANTITY * unitPrice);
                 char description[MAX_NAME_LENGTH];
                 sprintf(description, "%d for %f", x, offer->argument);
                 discount = discount_create(description, -discountTotal, &product);

common-lisp/source/receipt-printer.lisp

@@ -2,9 +2,21 @@
 
 (in-package :supermarket-receipt)
 
+;; Constants for receipt formatting
+(defconstant +default-columns+ 40)
+(defconstant +quantity-threshold+ 1.0)
+(defconstant +price-decimal-places+ 2)
+(defconstant +weight-decimal-places+ 3)
+
+;; Display strings
+(defconstant +unit-price-indent+ "  ")
+(defconstant +multiplication-symbol+ " * ")
+(defconstant +total-label+ "Total: ")
+(defconstant +whitespace-char+ " ")
+
 (defclass receipt-printer ()
   ((columns :initarg :columns
-            :initform 40
+            :initform +default-columns+
             :type integer
             :accessor printer-columns)))
 
@@ -22,35 +34,37 @@
   (let* ((total-price-printed (print-price a-printer (item-total-price an-item)))
          (name (product-name (item-product an-item)))
          (line (format-line-with-whitespace a-printer name total-price-printed)))
-    (unless (= 1.0 (item-quantity an-item))
-      (setf line (format nil "~A  ~A * ~A~%" line
+    (unless (= +quantity-threshold+ (item-quantity an-item))
+      (setf line (format nil "~A~A~A~A~A~%" line
+                         +unit-price-indent+
                          (print-price a-printer (item-price an-item))
+                         +multiplication-symbol+
                          (print-quantity a-printer an-item))))
     line))
 
 (defmethod format-line-with-whitespace ((a-printer receipt-printer) (a-name string) (a-value string))
   (let* ((line a-name)
          (whitespace-size (- (printer-columns a-printer) (length a-name) (length a-value))))
     (loop for index from 1 to whitespace-size do
-          (setf line (concatenate 'string line " ")))
+          (setf line (concatenate 'string line +whitespace-char+)))
     (setf line (concatenate 'string line a-value))
     (setf line (format nil "~A~%" line))
     line))
 
 (defmethod print-price ((a-printer receipt-printer) (a-price single-float))
-  (format nil "~2$" a-price))
+  (format nil (format nil "~~~d$" +price-decimal-places+) a-price))
 
 (defmethod print-quantity ((a-printer receipt-printer) (an-item receipt-item))
   (if (eq 'each (the-product-unit (item-product an-item)))
       (format nil "~d" (floor (item-quantity an-item)))
-      (format nil "~3$" (item-quantity an-item))))
+      (format nil (format nil "~~~d$" +weight-decimal-places+) (item-quantity an-item))))
 
 (defmethod print-discount ((a-printer receipt-printer) (a-discount discount))
   (let ((name (format nil "~A(~A)" (discount-description a-discount) (product-name (discounted-product a-discount))))
         (value (print-price a-printer (discount-amount a-discount))))
     (format-line-with-whitespace a-printer name value)))
 
 (defmethod present-total ((a-printer receipt-printer) (a-receipt receipt))
-  (let ((name "Total: ")
+  (let ((name +total-label+)
         (value (print-price a-printer (total-price a-receipt))))
     (format-line-with-whitespace a-printer name value)))

csharp/SupermarketReceipt.Test/ReceiptPrinter.cs

@@ -5,6 +5,19 @@ namespace SupermarketReceipt
 {
     public class ReceiptPrinter
     {
+        // Constants for receipt formatting
+        private const int DefaultColumns = 40;
+        private const int QuantityThreshold = 1;
+        private const int PriceDecimalPlaces = 2;
+        private const int WeightDecimalPlaces = 3;
+
+        // Display strings
+        private const string UnitPriceIndent = "  ";
+        private const string MultiplicationSymbol = " * ";
+        private const string TotalLabel = "Total: ";
+        private const string WhitespaceChar = " ";
+        private const string Newline = "\n";
+
         private static readonly CultureInfo Culture = CultureInfo.CreateSpecificCulture("en-GB");
 
         private readonly int _columns;
@@ -15,7 +28,7 @@ public ReceiptPrinter(int columns)
             _columns = columns;
         }
 
-        public ReceiptPrinter() : this(40)
+        public ReceiptPrinter() : this(DefaultColumns)
         {
         }
 
@@ -36,15 +49,15 @@ public string PrintReceipt(Receipt receipt)
             }
 
             {
-                result.Append("\n");
+                result.Append(Newline);
                 result.Append(PrintTotal(receipt));
             }
             return result.ToString();
         }
 
         private string PrintTotal(Receipt receipt)
         {
-            string name = "Total: ";
+            string name = TotalLabel;
             string value = PrintPrice(receipt.GetTotalPrice());
             return FormatLineWithWhitespace(name, value);
         }
@@ -62,9 +75,9 @@ private string PrintReceiptItem(ReceiptItem item)
             string totalPrice = PrintPrice(item.TotalPrice);
             string name = item.Product.Name;
             string line = FormatLineWithWhitespace(name, totalPrice);
-            if (item.Quantity != 1)
+            if (item.Quantity != QuantityThreshold)
             {
-                line += "  " + PrintPrice(item.Price) + " * " + PrintQuantity(item) + "\n";
+                line += UnitPriceIndent + PrintPrice(item.Price) + MultiplicationSymbol + PrintQuantity(item) + Newline;
             }
 
             return line;
@@ -77,23 +90,23 @@ private string FormatLineWithWhitespace(string name, string value)
             line.Append(name);
             int whitespaceSize = this._columns - name.Length - value.Length;
             for (int i = 0; i < whitespaceSize; i++) {
-                line.Append(" ");
+                line.Append(WhitespaceChar);
             }
             line.Append(value);
-            line.Append('\n');
+            line.Append(Newline);
             return line.ToString();
         }
 
         private string PrintPrice(double price)
         {
-            return price.ToString("N2", Culture);
+            return price.ToString("N" + PriceDecimalPlaces, Culture);
         }
 
         private static string PrintQuantity(ReceiptItem item)
         {
             return ProductUnit.Each == item.Product.Unit
                 ? ((int) item.Quantity).ToString()
-                : item.Quantity.ToString("N3", Culture);
+                : item.Quantity.ToString("N" + WeightDecimalPlaces, Culture);
         }
 
     }

go/go.mod

@@ -6,3 +6,10 @@ require (
 	github.com/approvals/go-approval-tests v0.0.0-20220530063708-32d5677069bd
 	golang.org/x/text v0.4.0
 )
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.11.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

go/go.sum

@@ -1,4 +1,13 @@
 github.com/approvals/go-approval-tests v0.0.0-20220530063708-32d5677069bd h1:8j7sBEy0h6+Bvr0AeKHIHCsmzCzWGXAQweA7k+uiRYk=
 github.com/approvals/go-approval-tests v0.0.0-20220530063708-32d5677069bd/go.mod h1:PJOqSY8IofNv3heAD6k8E7EfFS6okiSS9bSAasaAUME=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
+github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 golang.org/x/text v0.4.0 h1:BrVqGRd7+k1DiOgtnFvAkoQEWQvBc25ouMJM6429SFg=
 golang.org/x/text v0.4.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=